The Clostridial neurotoxins are a family of structurally similar proteins that target the neuronal machinery for synaptic vesicle exocytosis. Produced by anaerobic bacteria of the Clostridium genus, botulinum neurotoxins (“BoNT”s, seven immunologically distinct subtypes, A-G) and Tetanus neurotoxin (“TeNT”) are the most poisonous substances known on a per-weight basis, with an LD50 in the range of 0.5-2.5 ng/kg when administered by intravenous or intramuscular routes (National Institute of Occupational Safety and Health, “Registry of Toxic Effects of Chemical Substances (R-TECS),” Cincinnati, Ohio: National Institute of Occupational Safety and Health (1996)). BoNTs target cholinergic nerves at their neuromuscular junction, inhibiting acetylcholine release and causing peripheral neuromuscular blockade (Simpson, “Identification of the Major Steps in Botulinum Toxin Action,” Annu. Rev. Pharmacol. Toxicol. 44:167-193 (2004)).
A genetic engineering platform that enables rational design of therapeutic agents based on Clostridial toxin genes was described in U.S. Pat. No. 7,785,606 to Ichtchenko and Band. The genetic engineering scheme was based on a two-step approach. Gene constructs, expression systems, and purification schemes were designed that produce physiologically active, recombinant Clostridial neurotoxin derivatives. The recombinant toxin derivatives retained structural features important for developing therapeutic candidates, or useful biologic reagents. Using the genetic constructs and expression systems developed by this paradigm, selective point mutations were then introduced to create recombinant atoxic Clostridial neurotoxin derivatives.
Treatment methods that involve contacting a patient with isolated, physiologically active, toxic, Clostridial neurotoxin derivatives have been described in U.S. Pat. No. 7,785,606 to Band and Ichtchenko. Also, isolated, physiologically active, toxic and atoxic Clostridium botulinum neurotoxin derivatives that have an S6 peptide sequence fused to the N-terminus of the proteins to enable site-specific attachment of cargo using Sfp phosphopantetheinyl transferase have been described as suitable for treatment (U.S. Patent Application Publication No. 2011/0206616 to Ichtchenko and Band). However, methods that involve treatment with an atoxic derivative of a Clostridial neurotoxin lacking a cargo attachment sequence at its N-terminus, and having a much higher LD50 than a toxic derivative of a Clostridial neurotoxin or a wild type Clostridial neurotoxin, have not been described.
The present invention is directed to overcoming this and other limitations in the art.